Suxamethonium

Suxamethonium (succinylcholine) is a drug that is used for anaesthesia (muscle relaxant of the non - (competitive) depolarizing type). It is used for muscle relaxation during general anaesthesia.

Depolarizing muscle relaxants act as agonists (excitatory) of the_{NM nicotine receptor} on the motor endplate. The interaction with the receptor leads to a long-lasting depolarization of the motor endplate. Acetylcholine can no longer excite because the receptor channel is already open.

Depolarizing muscle relaxants such as suxamethonium (succinylcholine) are not degraded by acetylcholinesterase in contrast to acetylcholine. In this respect, the_NM nicotine receptor channel is opened in a long-lasting manner, the motor end plate remains depolarized in a long-lasting manner. This state of depolarisation is called depolarisation block, or phase I block.

The "multicentric" activation of the muscle fibres initially leads to a short contraction of the muscles. This can be observed in the patient as fasciculation of the muscles (uncoordinated muscle tremor). An exception to this is the eye muscles which can respond with a sustained contraction. The continuing depolarization prevents a renewed excitation by acetylcholine. This phase of uncoordinated fasciculation turns into a flaccid paralysis phase. The muscle is unexcitable. The effect cannot be reversed by other drugs (antagonizable).

Suxamethonium is broken down by an unspecific cholinesterase. This is produced in the liver. In the case of severe liver dysfunction or genetic disorders (0.05% of the European population), the breakdown is delayed. The patients must then be ventilated for hours (application of a purified serum cholinesterase is possible!).

The following frequency data shall be used for the evaluation of adverse reactions:

• very frequent: more than 1 treated person out of 10
• frequently: 1 to 10 treated from 100
• occasionally: 1 to 10 treated from 1.000
• rare: 1 to 10 treated from 10.000
• very rare: less than 1 treated person per 10.000
• not known: frequency not estimable on the basis of available data

Ocular NW: After administration of succinylcholine, the intraocular pressure is increased

Musculature: Frequently: Fasciculations of the musculature, postoperative muscle pain as well as cutaneous allergic reactions.

Cardiac NW: Occasionally: cardiac arrhythmias (ventricular arrhythmia, bradycardia with AV node replacement rhythm) occur.

Immunological NW: Anaphylaxis: rare: anaphylactic shock occurs after administration of succinylcholine.

Malignant hyperthermia: in individual cases succinylcholine may cause malignant hyperthermia or rhabdomyolysis.

Electrolytes: Hyperkalemia: leakage of potassium, creatinine phosphokinase and myoglobin from the muscle cell. This can lead to myoglobinuria and subsequent renal failure or acute heart failure in individual cases - mainly in adolescents.

Note: Overdosage of succinylcholine may prolong peripheral respiratory failure. The development of a Phase II block is expected to be dose- and time-dependent. Symptoms of overdose are more pronounced under the influence of alcohol and other central depressants.

Therapeutic measures for intoxication: Artificial respiration is required until the patient is able to breathe properly again. If necessary, purified cholinesterase preparations can be administered.

Suxamethonium is contraindicated in:

disposition to hyperkalemia (e.g. extensive burns, renal insufficiency, acute and chronic denervation syndromes)

• known hypersensitivity to other muscle relaxants,
• Presence of cholinesterase deficiency or defects,
• diseases of the neuromuscular system,
• penetrating eye injuries,
• Glaucoma.

Remark: An abnormal rigor of the muscle masseter may be an indication of an increased risk of rhabdomyolysis or malignant hyperthermia. Special intraoperative monitoring (e.g. capnometry) and avoidance of drugs that increase the risk (trigger substances) is recommended.

Succinylcholine may only be used by physicians who are familiar with its effects, who have mastered the methods and techniques of intubation, artificial respiration and resuscitation and who have the necessary equipment and medication. Neuromuscular function should be monitored intraoperatively using a nerve stimulator.

In all diseases of the neuromuscular system, increased sensitivity to succinylcholine must be expected; if necessary, a reduction in dose is necessary.

In the presence of an atypical cholinesterase variant, the effect may be prolonged, lasting up to hours (long-term ventilation necessary)

1. Kosinova M et al (2017) Rocuronium versus suxamethonium for rapid sequence induction of general anaesthesia for caesarean section: influence on neonatal outcomes. Int J Obstet Anesth 32:4-10.
2. Umesh G et al (2009) Suxamethonium stands the test of time: it is too early to say goodbye. Anaesthesia 64:1023
3. Zhang X et al (2019) Supramolecular therapeutics to treat the side effects induced by a depolarizing neuromuscular blocking agent. Theranostics 9:3107-3121.